Total internal reflection (TIR) is phenomenon that happens when a propagating wave (e.g., a light wave) hits a boundary of a medium (e.g., glass, acrylic, etc.) at an angle greater than a particular critical angle with respect to a normal of a surface of the medium. For TIR to occur, if a refractive index is lower on an opposite side of a boundary from which the wave is hitting the boundary and the incident angle is greater than the critical angle, the wave cannot pass through the boundary and is entirely reflected within the medium.
The figures are not to scale. Instead, to clarify multiple layers and regions, the thickness of the layers may be enlarged in the drawings. Wherever possible, the same reference numbers will be used throughout the drawing(s) and accompanying written description to refer to the same or like parts. As used in this patent, stating that any part (e.g., a layer, film, area, or plate) is in any way positioned on (e.g., positioned on, located on, disposed on, or formed on, etc.) another part, means that the referenced part is either in contact with the other part, or that the referenced part is above the other part with at least one intermediate part located therebetween. Stating that any part or object is in contact with another part or object means that there is no intermediate part or space between the part(s) or object(s).